1. Field of the Invention
The present invention relates to a structure and manufacturing method of gallium nitride (GaN)-based light emitting component, especially the structure and manufacturing method of a kind of light emitting diode. The light emitting diode comprises a transparent conductive window layer comprising a domain contact layer, a diffusion barrier layer, and a window layer.
2. Description of the Related Art
In the conventional art, the formed gallium nitride (GaN)-based light emitting diode by using the sapphire substrate as shown in FIG. 1, therein, includes a gallium nitride buffer layer 2, a N-type gallium nitride ohmic contact layer 3, an indium gallium nitride light emitting layer 4, a P-typer aluminum gallium nitride cladding layer 5, and a P-type gallium nitride ohmic contact layer 6, subsequently crystallizing on a sapphire substrate 1, and, at last, with a P-type transparent metallic conductive layer 7 formed on the P-type GaN ohmic contact layer 6, an anode electrode bonding pad 8 on the transparent metallic conductive layer 7, and a cathode electrode bonding pad 9 on the N-type GaN contact layer 3. Because of the population of the specific refraction of the crystalline structure of the GaN multi-layer (n=2.4), the sapphire layer (n=1.77), and the cladding resin material in packing (n=1.5), there is only 25% of the light coming from the light emitting layer that that can be emitted at once without being refracted by the interface; whereas, the left 75% of the light is strained by the light inductive structure configured by the sapphire substrate and the cladding resin used in packing, thus prompting the probability of re-absorbing of the light and causing the inefficiency of usage. Therefore, the extraction mechanism of the light emitting diode structure is subject to the absorption of the transparent metallic conductive layer and the re-absorption of the internal structure of the crystal.
In addition, the conductivity of the P-type GaN ohmic contact layer is very poor. Generally, the electric resistivity locates at 1˜2 Ωcm, and the thickness is around 0.1˜0.5 μm. In other word, the current would easily be contained under the P-type metal electrode 8; therein the cross-sectional distance of distribution is around 1 μm. Thus, to spread the current efficiently, first of all, the transparent metal conductive layer 7 must be formed on the P-type GaN ohmic contact layer 6 and be scattered on the whole luminous area, and to advance the transparency, the transparent metal conductive layer 7 must be very thin. Generally, the transparent metal conductive layer 7 is formed of the Ni/Au with the thickness between 50˜500 Å.
According to the conventional art, the study about the transparent metal conductive layer formed of the Ni/Au, to decrease the operating voltage of the light emitting diode, it is necessary to lower down the contact resistivity of metal conductive layer and the P-type GaN ohmic contact layer to 10−4 Ωcm2. And to increase the efficiency of the external quantum, it ought to be good that the transparency of the metal conductive layer must be higher than 80% with the visible wavelength of light between 400 nm˜700 nm. As the disclosure on the P. 1275 of the Applied Physic letters vol. 74(1999), the sample was placed in the oxidization environment to be annealed so as to facilitate the constituting of the middle layer of NiO semiconductor layer to lower down the contact resistivity and advance the transparency. Additionally, according to the disclosure of the study on p. 1741 of Solid-state Electronic 47(2003), to advance the transparency efficiently, it is better with the Ni and Au as thin as available in thickness, whereas, to lower down the contact resistivity, it is better with the Au as thick as possible. Hence, there are still the above-mentioned constraints to utilize the Ni/Au as transparent metal conductive layer of GaN-based light emitting diode.
Furthermore, the Taiwan patent No. 461126 shows a kind of structure of GaN-based light emitting diode as exhibited in FIG. 2, wherein the light emitting diode 10 includes a substrate 110′, a n-GaN 120′, a n-AlGaN 130′, an u-InGaN 140′, a p-AlGaN 150′, a p-GaN 160′, a high carrier concentration layer 170′, and a transparent conductive layer 180′.
The transparent conductive layer 180′ is connected and mixed with p-GaN 160′ by high heart treatment, which is not easily to form a good ohmic contact, thus without the efficient plunging operating voltage of the light emitting diode. Besides, an additional layer 170′ such as Ni/Au or Ni/Cr metal can be put between the transparent conductive layer 180′ and the p-GaN 160′ so as to lower down the operating voltage efficiently. However, according to the personal study, while applying Ni/Au on the structure of the transparent conductive layer, specially on the Indium Tin Oxide, the Au—In mixer with high resistance formed on the interface between the Ni/Au and the Indium Tin Oxide would contribute to the inefficiency of lowering down the operating voltage of the component and the poor transparency in whole because of the easily diffusing of Indium from the Indium Tin Oxide transparent conductive layer in the manufacturing process.
In addition, the U.S. Pat. No. 6,420,736 also disclosed a kind of window layer structure of GaN-based light emitting diode as shown in FIG. 3, wherein, the light emitting diode includes a sapphire substrate 210′, a buffer layer 220′, a n-GaN layer 230′, a n-cladding layer 240′, an active layer 250′, a p-cladding layer 260′, a window layer 270′ and 280′, a NiOx/Au layer 290′, and a transparent conductive layer 300′. Therein, the NiOx/Au layer was used to form the ohmic contact with the p-cladding layer 260′, and then the transparent conductive layer 300′ was utilized as current spreading and transparent layer. According to the personal study, while using the NiOx/Au as ohmic contact layer, it is still inevitable that the Au—In mixer with high resistance would be formed in the process of manufacturing, so the operating voltage of the components can not be lowered down efficiently, and the transparency in whole would fall easily.
Therefore, to propose the solution of the novel GaN-based light emitting diode structure and manufacturing mehtod, always the expectation and concern of the inventor, to the above-mentioned problem not only can improve the failure of lowering down the operating voltage in the conventional light emitting diode, but also advance the whole transparency. Because of engagement in the personal study, invention, and the sales experience for many years, the intention of improving has been in embryo, and finally the structure and improved manufacturing of kind of GaN-based light emitting diode to the above-mentioned problem has been figured out.